Hollow glass article with improved optical finish

ABSTRACT

A hollow glass article having an improved optical finish which is formed by placing a molten material in the original article while it is constrained in a mold. The molten material softens the glass and produces a hydrostatic pressure which reforms the article into the finished shape by expanding the original glass article to the shape of the mold.

This application is a division of application Ser. No. 029,310, filedApr. 12, 1979, now U.S. Pat. No. 4,295,873, granted Oct. 20, 1981.

The present invention relates to a method and apparatus for reworking ahollow workpiece to a desired dimensional accuracy and optical finish.The invention may advantageously be employed with bulbs such as thoseutilized for incandescent lamp bulbs.

In the conventional manufacturing technique, bulbs for incandescentlamps are blown in molds which are lined with a suitable layer ofcarbonizing material such as ground cork in an appropriate binder.However, serious disadvantages are inherent in the conventional bulbmanufacturing technique. For example, it is difficult to apply andmaintain the layer of carbonizing material either at a uniform thicknessor accurately in relation to the axis of the bulb. Thus, bulbs producedin accordance with conventional techniques depart considerably fromdesired dimensions and contours. The variability in dimension ofconventional incandescent lamp bulbs has not had a serious detrimentaleffect on their operation since conventional incandescent lamps merelyrequire that the bulbs have sufficient transparency to allow passagetherethrough of light emitted by the filament.

However, coatings capable of transmitting the visible portion of theelectromagnetic radiation produced by the filament while at the sametime reflecting radiation corresponding to the infrared portion of thespectrum are now available. In lamps with such coatings, reflection ofinfrared radiation back to the filament heats the filament and therebyincreases the efficiency of the incandescent bulb. This results inenergy conservation and reduced operating costs. Such a lamp isdescribed in U.S. patent application Ser. No. 781,355, filed Mar. 25,1977, now U.S. Pat. No. 4,160,929 which is assigned to the assignee ofthe subject application. The usefulness of such coatings is increased ifthe reflected infrared rays are accurately focused onto the filament.This can be accomplished by making the bulb of a desired opticalreflecting shape, e.g. spherical or elliptical, and more opticallyperfect to reflect the IR energy to the filament. Heretofore, thevariability in dimension and contour of the bulb has made it difficultto have a bulb which can accurately reflect infrared rays emitted fromthe filament back onto the filament. Accordingly, it is an object of thepresent invention to provide a method and apparatus for reworking bulbsto a higher degree of optical accuracy so that the bulb, afterapplication of suitable coatings, is better capable of reflectingradiation to a predetermined location in the interior of the bulb. It isalso a further object of the present invention to provide a method andapparatus for imparting an improved optical finish to bulbs.

BRIEF SUMMARY OF THE PRESENT INVENTION

In accordance with the present invention, a method and apparatus forreworking a hollow workpiece, such as a glass bulb, to a desireddimensional accuracy is provided. Fluid, illustratively molten metal, ofa temperature sufficient to soften the bulb material is poured into aworkpiece which is disposed within a mold of desired dimensions. Thefluid is of sufficient density so that the static pressure of the fluidcauses the softened bulb to contact the mold and thereby take on thedimensions of the mold. The softened workpiece is then cooled so thatthe workpiece may be handled without deforming.

Heretofore, floating of glass on a bath of molten metal has beenutilized to produce sheets of flat glass. U.S. Pat. Nos. 3,083,551 and3,222,154 to L. A. B. Pilkington teach a method of manufacturing flatglass wherein glass is introduced to a bath of molten metal oftemperature sufficient to melt the glass. The molten glass advancesalong the bath of molten metal and flows laterally across the bath untilit reaches a condition of equilibrium and stable thickness. The moltenglass continues to move along the bath and is sufficiently cooled sothat it may be removed from the bath by mechanical means as a sheet offlat glass. However, Pilkington only teaches flotation of molten glasson a bath of molten metal to produce a sheet of flat glass.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the present invention reference is madeto the accompanying drawings in which:

FIG. 1 is a front elevational view of a preferred embodiment of theapparatus in accordance with the present invention;

FIG. 2 is a side elevational view of a portion of the apparatus of FIG.1;

FIG. 3 is a front elevational view of the apparatus of FIG. 1 with themold portions in closed position and further depicting a reservoirhaving a vertically displaceable extension tube.

FIG. 4 is a front elevational view of the apparatus of FIG. 1 showing analternative embodiment of the reservoir;

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings, and in particular to FIG. 1, theapparatus is generally designated 10. A mold 20, having a cavity 24 ofdesired contour and dimension, is separable into two mold portions 21a,21b. As depicted, mold portions 21a, 21b are mirror images of oneanother. However, it should be understood that the mold may take avariety of alternative forms. For example, the mold may comprise aplurality of symmetric or non-symmetric members capable of being joinedto define the desired mold cavity shape. Hollow workpiece 11, of anydesired shape, but preferably of a shape generally conforming to that ofthe mold, is introduced into cavity 24 of mold 20 by separating moldportions 21a, 21b, aligning workpiece 11 with cavity 24 and thenenclosing mold portions 21a, 21b around workpiece 11. The mold cavity 24is slightly larger than the raw workpiece so that the workpiece is notdamaged when the mold portions 21a,21b are enclosed. As depicted in FIG.1, workpiece 11 comprises a bulb having a generally spherical portion 12terminating in a tubular portion 13. Mold cavity 24 has a shapecorresponding with workpiece 11.

In the preferred embodiment, the dimensional accuracy of mold cavity 24is made such as to be able to produce a bulb 11 capable of accuratelyreflecting radiation emitted from a filament back to the filament.

Each mold portion 21a, 21b is mounted to a corresponding mold support31a, 31b so that both mold portions 21a, 21b may be rotated about acommon horizontal axis which approximately passes through a horizontaldiameter of spherical portion 12 of bulb 11. It should be understood,however, that the axis about which mold 20 rotates need not pass througha diameter of spherical portion 12 of bulb 11.

Mold portions 21a, 21b are rotatably mounted to mold supports 31a, 31bby respective shafts 14a, 14b extending from each mold portion 21a, 21band seated within channels provided in mold supports 31a, 31b. Suitablebearings may be utilized to minimize frictional resistance. Shafts 14a,14b run through mold supports 31a, 31b and are each affixed to arespective pinion gear 40a, 40b. Thus, each mold portion 21a, 21brotates about a common horizontal axis in fixed relation with therespective pinion gear 40a, 40b.

Segment gears 41a, 41b are rotatably mounted on brackets 43a, 43baffixed to a frame 30. Segment gears 41a, 41b are affixed to a commonshaft 46 so that segment gear 41a moves in fixed relationship withsegment gear 41b. As seen in FIG. 2, segment gear 41a is mounted tobracket 43a at an intermediate position of segment gear 41a. At one end,segment gear 41a is affixed to piston rod 45 of pneumatic cylinder 42a.Upon actuation and lowering of piston rod 45, segment gears 41a, 41brotate about shaft 46. Teeth on segment gears 41a, 41b intermesh withteeth of the corresponding pinion gears 40a, 40b. The lowering of pistonrod 45 results in upward displacement of the toothed portion of segmentgears 41a, 41b. This in turn causes pinion gears 40a, 40b and moldportions 21a, 21b to rotate downwardly in the direction of arrow 80.

As shown in FIG. 1, each respective mold portion 21a, 21b is providedwith gearing 40a, 40b, 41a, 41b capable of rotating respective moldportion 21a, 21b. Mold portions 21a, 21b are rotated together and infixed relationship to one another to prevent relative motion between themold portions 21a, 21b. Any relative motion between respective moldportions 21a, 21b would produce undesirable stress and possible breakageof the workpiece 11 contained within cavity 24 of mold 20. Accordingly,in the present embodiment, segment gears 41a, 41b are affixed to acommon shaft 46 so that segment gears 41a, 41b rotate in fixedrelationship to one another. It should be apparent, however, that avariety of alternative mechanisms may be provided to rotate moldportions 21a, 21b in unison. For example, mold portions 21a, 21b may beurged together with pressure sufficient to prevent relative motionbetween the mold portions 21a, 21b at the point where they contact eachother. Thus, by rotating one of mold portions 21a, 21b, the remainingmold portion 21b, 21a will also rotate.

In combination with the axial rotating means, mold portions 21a, 21b arelaterally separated to allow placement therebetween of workpiece 11.Mold supports 31a, 31b are provided with guides 33a, 33b which areslidably seated on tracks 32a, 32b mounted to frame 30. Thus, moldsupports 31a, 31b and their rotatably fixed mold portions 21a, 21b aredisplaceable along the path of tracks 32a, 32b. As shown in FIG. 2,guides 33a, 33b are depicted as generally C-shaped members and tracks32a, 32b are depicted as generally T-shaped members having rectangularupper portions. In the preferred embodiment, tracks 32a, 32b are mountedto frame 30 along a common longitudinal axis so that upon inwarddisplacement, mold portions 21a, 21b come together in proper alignmentto define a continuous cavity 24. Furthermore, adjoining faces of moldportions 21a, 21b are fitted to one another to avoid creation of a seamat the interface of mold portions 21a, 21b.

To achieve proper alignment of mold portions 21a, 21b, each must track awell-defined path. Any free play, in either the vertical or horizontalaxes, may result in undesirable misalignment of the mold portions. Inthe present invention, the arrangement of C-shaped guides 33a, 33b whichslidably mate with T-shaped tracks 32a, 32b advantageously avoids freeplay in either the horizontal or vertical directions. As seen in FIG. 2,the top and bottom walls of guides 33a, 33b prevent verticaldisplacement of mold supports 31a, 31b while the side walls of guides33a, 33b prevent horizontal displacement.

Mold portions 21a, 21b are displaced along their respective tracks 32a,32b by a pair of lever arms 34a, 34b. Each lever arm 34a, 34b ispivotally mounted to a bracket 78a, 78b at pivot 77a, 77b. Lever arms34a, 34b each comprise a generally T-shaped member. A slotted end 35a,35b of lever arm 34a, 34b engages a pin 38a, 38b affixed to mold support31a, 31b and segment gear 36a on lever arm 34a intermesh with segmentgear 36b on corresponding lever arm 34b. The lower end 39a, 39b of eachrespective lever arm 34a, 34b is connected to a cylinder 37. Uponextension of the piston of cylinder 37, the respective slotted ends 35a,35b move inwardly bringing mold portions 21a, 21b into contact. Thealignment of tracks 32a, 32b along a common longitudinal axis and theutilization of C-shaped guides 33a, 33b bring mold portions 21a, 21btogether in horizontal and vertical alignment. It should be understoodhowever that a variety of alternative arrangements may be utilized toeffect vertical and horizontal alignment of mold portions 21a, 21b. Forexample, mold portion 21a may have indentations and/or protrusions whichmate with corresponding protrusions and/or indentations on the othermold portion 21b.

Separation of the respective mold portions 21a, 21b is effected byretracting the piston of cylinder 37. This causes slotted ends 35a, 35bof lever arms 36a, 36b to move away from each other, thus separating therespective mold portions 21a, 21b.

In combination with mold 20, reservoirs or tanks 50 are provided. Asseen in FIG. 3, each reservoir 50, is supported by support members 71,72 and 73. A lever 54 is pivotably mounted, at an intermediate portionthereof, to bracket 75 affixed to support member 73. One end of lever 54is connected to the rod of a hydraulic cylinder 76 mounted on supportmember 72 by bracket 74. At the opposite end of lever 54, rod 51 extendsvertically downward through reservoir 50. At its lowermost portion, rod51 is connected to a plug 52 fitted within seat 53 at a lower portion ofreservoir 50. Extension of cylinder 76 moves rod 51 downwardly so thatplug 52 is urged against seat 53, creating a seal which shuts off thesupply of fluid contained within reservoir 50. Tube 57 extendsdownwardly from spout 56 of reservoir 50. An extension tube 58, slidablyfitted to tube 57, is capable of telescoping from tube 57 to provide adownwardly extending extension for tube 57. In FIG. 3 the solid linesdepict extension tube 58 in a full down position and the dotted linesdepict extension tube 58 in a full up position. Tube 58 has an outerdiameter smaller than the inner diameter of the narrowest part oftubular portion 13 of bulb 11. Thus it is possible to extend extensiontube 58 to the bottom of a spherical portion 12 of bulb 11. Verticaldisplacement of extension tube 58 is achieved by an arm 59 affixed to anupper portion of extension tube 58. An opposite end of arm 59 is affixedto a rod 61 which is vertically displaceable by means of cylinder 62.

In an alternative embodiment (FIG. 4), reservoir 50 empties out directlythrough tube 57. In this embodiment, the lowermost opening of tube 57 isvertically aligned with the opening of mold 20. On lifting plug 52,fluid contained within reservoir 50 falls directly into the center ofworkpiece 11.

In the preferred embodiment, heating elements are utilized to heat themold 20 and tank 50. Heating elements 63 are provided around theperimeter of each reservoir 50. Each mold portion 21a, 21b is providedwith channels 26a, 26b running therethrough. Electrical heating elementsof a conventional type are inserted within the channels.

The heating elements are connected by conventional wires 25a, 25b to acompatible power source. It should be apparent however that the heatingmeans may take a variety of alternative forms, electrical or otherwise.

The operation of the apparatus and the method in accordance with thepresent invention is now described. As shown in FIG. 1, apparatus 10 isarranged with mold portions 21a, 21b separated. Mold portions 21a, 21bare stabilized at a desired temperature by utilization of conventionalheating means disposed within channels 26 of mold portions 21a, 21b. Fora glass workpiece, the molds are stabilized at approximately 650° C.(hereinafter °C.). The mold is purged with an inert gas to minimizeoxidation of the fluid, illustratively molten metal which is introducedinto the interior of workpiece 11. A gas supply of any conventional typemay be utilized. In the preferred embodiment, the inert gas comprisesnitrogen gas. After purging of the mold, a raw workpiece 11,illustratively a lamp bulb, is suspended in alignment with cavity 24 ofmold 20. Raw workpiece 11 generally has imperfections in its dimensionsand contours. Mold portions 21a, 21b are joined to contain raw workpiece11 within mold cavity 24. It should be apparent to those skilled in theart, that the mechanism for suspending workpiece 11 in alignment withcavity 24 of mold 20 may take a variety of alternative forms. Forexample, workpiece 11 may be supported by a member (not shown) havingexpandable fingers which extend through tubular portion 13 of workpiece11 gripping an interior portion of bulb 11 and retaining the bulb inalignment with mold portions 21a, 21b.

The mold portions 21a, 21b are joined together by actuation andextension of the piston of cylinder 37. This causes lever arms 34a, 34bto rotate bringing the slotted ends 35a, 35b of each lever arm 34a, 34band the respective mold portions 21a, 21b inward.

After mold portions 21a, 21b close over workpiece 11, workpiece 11 ispurged by an inert gas jet, preferably nitrogen, which advantageouslyminimizes oxidation of the fluid, illustratively molten metal, which isintroduced into the interior of workpiece 11.

Mold 20 is then brought into vertical alignment with a first reservoir50 (FIG. 3) so that extension tube 58 is aligned with the opening ofmold 20 and workpiece 11. The first reservoir 50 contains fluid of atemperature sufficiently high to soften the workpiece and of densitysufficient to exert static pressure on the workpiece to bring theworkpiece into contact with the mold. Heating elements 63 advantageouslysupply the necessary heat. In a preferred embodiment, the workpiece 11comprises a lamp bulb of glass construction. For such a workpiece, afluid of approximately 900° C. will adequately soften the glass bulb.Molten tin of approximately 900° C. advantageously provides both desiredfluidity and sufficient density to force the softened glass into contactwith the interior surface of mold 20.

After vertically aligning extension tube 58 with tubular portion 13 ofbulb 11, cylinder 62 is actuated to bring extension tube 58 into theinterior of lamp bulb 11. Since the outer diameter of extension tube 58is less than the inner diameter of the narrowest portion of tubularportion 13 of bulb 11, extension tube 58 enters the interior ofworkpiece 11 unhindered. After extension tube 58 is lowered into theinterior of workpiece 11, outlet 60 is located near the bottom ofspherical portion 12 of bulb 11 (FIG. 3).

The high temperature fluid (first charge) is introduced into theinterior of the workpiece 11 by actuating cylinder 76. As shown in FIG.3, actuation of cylinder 76 lifts plug 52 from seat 53 and allows thehigh temperature fluid to flow through outlet 60 into the interior ofworkpiece 11. After introduction of the high temperature fluid intoworkpiece 11, cylinder 62 is again actuated to raise extension tube 58out of workpiece 11. Introduction of the high temperature fluid into theinterior of workpiece 11 from outlet 60 of extension tube 58 located ata lower interior portion of the workpiece advantageously avoidsundesirable splashing and hammering effects which can otherwise occur iffluid is allowed to freely fall into the interior of workpiece 11 fromabove.

It should be apparent that the alternative embodiment in accordance withFIG. 4 may be utilized to introduce high temperature fluid from tube 57directly to workpiece 11 in instances where the freely falling fluiddoes not create undesirable splashing and hammering effects.

An annular gutter 22 encompassing the top portion of mold 20 catchesexcess molten tin and directs it through a spill pipe 23 for collectionon collection trough 27. The high temperature of the molten tin softensthe glass and the static pressure of the molten tin forces the glassinto contact with the interior surface of mold cavity 24. Thus,imperfections in the dimensions of the raw lamp bulb 11 are eliminatedsince the softened lamp bulb takes on the dimensions of the interiorsurface of mold cavity 24.

After it is softened and takes on the dimensions of the interior surfaceof mold cavity 24, workpiece 11 is sufficiently cooled so that it can behandled without deforming. In the preferred embodiment, the workpiece iscooled by introducing fluid of a temperature lower than the hightemperature fluid into the workpiece. However, it should be apparentthat cooling of the workpiece can be accomplished in a variety ofalternative ways.

In the preferred embodiment, apparatus 10, containing workpiece 11filled with fluid of temperature sufficiently high to soften theworkpiece, is aligned with a second reservoir 50 in accordance with FIG.3. The second reservoir 50 is of similar or identical construction tothe first reservoir 50. It will be apparent that in aligning apparatus10 with the first and second reservoirs 50 that either the apparatus orthe reservoirs can be moved. The second reservoir 50 is provided with avertically displaceable extension tube 58 which telescopes from theoutlet end of tube 57. Displacement of extension tube 58 is controlledby a lever arm 59 responsively connected to rod 61 of cylinder 62. Theouter diameter of extension tube 58 is less than the inner diameter ofthe narrowest portion of tubular portion 13 of bulb 11.

After aligning extension tube 58 with tubular portion 13 of bulb 11,cylinder 62 is actuated to bring extension tube 58 into the interior oflamp bulb 11 which is filled with high temperature fluid. As shown inFIG. 3, upon actuation of cylinder 62, the outlet 60 of extension tube58 is located near the bottom of spherical portion 12 of bulb 11.

Fluid in the second reservoir 50 is maintained at a lower temperaturethan in the first reservoir. In the present embodiment, the secondreservoir contains molten tin of approximately 650° C. Heating meanssuch as those utilized with the first reservoir 50 may be utilized tomaintain the fluid in the second reservoir at a desired temperature.Upon actuation of cylinder 76 and lifting of plug 52 from seat 53, themolten tin of 650° C. flows through tube 57, extension tube 58 andoutlet 60 of extension 58. As the molten tin flows into the lowerportion of workpiece 11, it displaces the high temperature fluid out ofworkpiece 11. The high temperature molten tin overflows the top oftubular portion 13 of bulb 11 and enters annular gutter 22 of mold 20and spillpipe 23 for removal via collection trough 27. The overflow mayadvantageously be recycled to either the first or second reservoirs.

The molten tin of lower temperature (second charge) displaces the hightemperature molten tin from the workpiece and cools the glass bulbsufficiently so that it may be handled without deforming. After bulb 11is filled with the lower temperature tin, cylinder 62 is again actuatedto bring extension tube 58 out from the interior of bulb 11. Aftercooling the bulb, the contained fluid is decanted by actuating cylinder42 to rotate mold 20 downwardly as shown in FIG. 2. During the initialstages of the downward rotation, fluid contained within the interior ofbulb 11 flows through spillpipe 23 and onto collection trough 27.However, as the angular rotation increases, fluid contained within theinterior of bulb 11 begins to pour directly from the rim of the annulargutter 22 to collection trough 27 bypassing spillpipe 23. Bulb 11shrinks slightly during cooling so that, in the cool state, mold cavity24 is slightly larger than bulb 11.

It should be apparent that the composition and temperature of the highand lower temperature fluids will vary depending on the composition ofthe workpiece utilized. Accordingly, the reference to molten tin ofapproximately 650° C. and 900° C. is by way of illustration for glassbulbs.

A stop 44 of conventional type may be utilized to define the limits ofthe arcuate path of rotating mold 20. After any contained fluid isremoved from the interior of the workpiece, the reworked workpiece isremoved from mold 20 by separation of mold portions 21a, 21b. Amechanism of any conventional type may be utilized to retain theworkpiece in place while mold portions 21a, 21b are separated. Aspreviously indicated, a member having expandable fingers may be insertedinto the hollow interior of the workpiece with its fingers retracted.Once inside the workpiece, expansion of the fingers against the interiorwalls of the workpiece retains the same in place. It should beunderstood that removal of the workpiece from the mold can take placewhile the workpiece is in the downwardly rotated position, in the fullvertical position, or at any intermediate position therebetween.

The method and apparatus in accordance with the present invention iseasily adapted to conventional manufacturing techniques. For example, aneconomical assembly line production method utilizes a plurality ofapparatuses 10 arranged around a circular turntable. Illustratively, themethod in accordance with the present invention may be performed ateight stations with utilization of eight apparatuses 11 arranged on aturntable. At each position a single operation is performed and uponcompletion of the operation the turntable rotates bringing eachapparatus 11 to a new station where the next step is performed. Thus,eight different operations are performed simultaneously.

Illustratively, operations performed with an eight station setup wouldbe as follows. At position one, the mold is purged with inert gas underpressure, the workpiece 11 is loaded by the operator and the moldportions 21a, 21b are closed over the workpiece 11.

The apparatus 11 then moves on to position 2 where the interior ofworkpiece 11 is purged of air by use of an inert gas jet.

At position 3, the mold is aligned with a first reservoir 50 inaccordance with FIG. 3. Extension tube 58 is lowered into the interiorof workpiece 11 by actuation of cylinder 62 and fluid of temperaturesufficiently high to soften the workpiece is introduced into theinterior of bulb 11 from the reservoir. After workpiece 11 is chargedwith high temperature fluid, extension tube 58 is raised out ofworkpiece 11.

At position 4, heat transfer from the high temperature fluid to theworkpiece softens the workpiece. The static pressure of the fluid forcesthe workpiece, illustratively glass, into contact with the interiorsurface of the mold 20.

At position 5, the mold is aligned with a second reservoir 50 inaccordance with FIG. 3. Cylinder 62 is actuated bringing extension tube58 into the interior of bulb 11 and fluid of lower temperature isintroduced into the interior of bulb 11 at the outlet 60 of extensiontube 58 located near the bottom of spherical portion 13 of bulb 11. Theoverflow of high temperature fluid is directed through spillpipe 23 andonto collection trough 27 for recycling.

At position 6, the lower temperature fluid reduces the temperature ofthe glass sufficiently to allow handling without deformation.

At position 7, mold 20 is downwardly rotated to decant the molten tinonto a collection trough 27.

Finally, at position 8 the mold opens and the reworked bulb is removed.The apparatus 10 returns to position 1 with the mold portions 21a, 21bopen and ready to receive another workpiece 11.

It should be apparent that the present invention may take a variety ofalternatve forms and that the foregoing description is merelyillustrative. Accordingly, the scope of protection afforded the presentinvention is defined by the annexed claims.

What is claimed is:
 1. A hollow glass article of improved optical finishformed by depositing in the original article constrained in a moldthrough an opening therein a molten liquid material of a temperaturesufficient to soften the glass and produce a hydrostatic pressuretherein which reforms the original article into the finished article byexpanding the original article to the shape of the mold.
 2. A hollowglass article as in claim 1 wherein the article is formed by removingthe first named molten liquid and depositing a second liquid of a lowertemperature which permits the glass to harden.
 3. A hollow glass articleas in claim 1 whose major portion is generally spherical.
 4. A hollowglass article as in claim 1 wherein the molten liquid material depositedin the original article is a metal.